The Five Kinds of Friends You Need

Robin Dunbar, the evolutionary psychologist behind the famous "Dunbar's number," spent decades proving that human beings can only maintain about 150 meaningful relationships at once.

They exist in distinct layers, and each layer has a completely different job in your life.

In my book MODERN FRIENDSHIP, I gave those layers water-y names to highlight how fluid these tiers are:

• The Bathtub (1-2 people)

• The Jacuzzi (3-5 people)

• The Swimming Pool (10-15 people)

• The Beach Bonfire (~50 people)

• The Water Park (~150 people)

Do I have an aesthetically pleasing graphic of these tiers? I’m so glad you asked! I do!

To be clear, these numbers are based on Robin Dunbar’s research. I just named ‘em!

People dip in and out of these tiers throughout our adult lives for all sorts of reasons. My book obsessively lays out what those reasons are. (So if you’ve ever been baffled about why a friendship ended, I’ll help you diagnose the reason so you can finally get peace).

Let’s learn more about these friends.

The Bathtub (1-2 people)

This is your most intimate tier — a partner, a best friend, sometimes both. These are the people who know the unedited version of you, who you’d call with genuinely bad news, who would notice within days if something was wrong. Lose someone from this tier and you feel it in your bones. Most people have had a bathtub relationship collapse at some point and remember exactly what that absence felt like.

The Jacuzzi (3-5 people)

Still warm, still close, but a little more room. These are your ride-or-dies — the friends who show up, who remember things, who you see regularly enough that your life feels woven together with theirs. You’ve spent over 200+ hours together. A strong Jacuzzi is one of the best predictors of long-term wellbeing, which is why it’s also the tier most likely to shift during major life transitions like a move, a new job, or a serious relationship.

The Swimming Pool (10-15 people)

You care about these people and they care about you, but the relationship has some conditions attached — shared history, proximity, a recurring context like a book club or a neighborhood. When that context disappears, swimming pool friendships often go with it. That’s not a failure. It’s just how this tier works.

The Beach Bonfire (~50 people)

You know their names, their general deal, maybe their kids’ names. You’d be genuinely happy to run into them. But you’re not tracking each other’s lives closely, and that’s fine — this tier exists for warmth and weak ties, not deep support.

The Water Park (~150 people)

Dunbar’s research suggests this is roughly the cognitive limit for social recognition. Beyond it, faces start to blur.

Most friendship advice focuses on the water park. Grow your network. Put yourself out there. Meet new people. And yes, a full water park has its uses — weak ties are how you find jobs, apartments, recommendations, opportunities. But weak ties cannot hold you when something goes wrong. They cannot notice when you’ve gone quiet. They cannot sit with you in the particular way that only someone who truly knows you can.

The loneliness epidemic isn’t really a water park problem. Most lonely people have an overflowing cornucopia of acquaintances. What they’re missing are those valuable Jacuzzi people. Or they had Jacuzzi people but the tier has been emptying for years — friends who moved away and their role in your life hasn’t been filled, relationships that drifted due to changing priorities, a marriage that absorbed all available social energy — and they haven’t noticed until something forced them to look. A job loss or death. A divorce or a move.

This is the thing about the tiers: they require different kinds of maintenance. The water park mostly takes care of itself. Show up at places, be reasonably warm, and, attend those weddings and funerals to interact with these far-flung connections. The beach bonfire needs occasional tending — a text here, a wave there. But the bathtub and the Jacuzzi require real investment.

Random notes:

• Trader Joe’s has a new Vitamin C serum for $9.99 and it appears to be a Skinceuticals dupe. I picked it up over the weekend. It smells horrible and it’s watery, which are good signs. Vitamin C serums should smell like hot dog water! I’ve been VERY into their new dupes for higher-end products. The marula oil cleaner. The dewy serum. I want to get lunch with whoever is heading up this product category for the store. I’ll bet they’re awesome!

• I’ve been watching “For All Mankind” season 5. If you think about the premise for more than five seconds, the whole thing falls apart. Are there only a handful of families in existence that can head up interstellar space missions?? Who gets pregnant in space and chooses to raise their kid on Mars?? But, I love this ridiculous soap opera X space flight mashup.

• My husband got food poisoning this weekend, which sucks for him. But I’ve been living my best Girl Dinner life since he has zero appetite. Handfuls of berries. A package of smoked salmon. Crackers and hummus. No real dishes to do!

• I also watched the whole second season of “Last One Laughing UK” (Prime) on Saturday and I laughed so hard that I convulsed. Watching that show feels like hanging out with your funniest friends for a few hours.

Has this Bathtub framework helped you? Does having more specific names for these tiers help make friendships feel more manageable? Tell me in the comments.